1. Field of the Invention
The present invention relates to a polyamide composition useful in the production of lightweight shaped articles. In another aspect, this invention relates to a polyamide composition which contains a pore-forming agent. This invention also relates to a process for preparing the subject polyamide composition. In yet another aspect, the invention relates to a shaped article made from a modified polyamide, such modification comprising the incorporation therein of a minor amount of a masterbatch polyamide composition containing a conventional pore-forming agent.
2. Description of the Prior Art
The U.S. Pat. No. 4,076,667, assigned to the assignee hereof, discloses granules comprising a polycondensate in powder form, a fusible binder having a melting point of 70.degree.-100.degree. C. and which is compatible with the polycondensate and a dyestuff or compound capable of modifying the polycondensate to be shaped. The problems faced when attempting to modify the structure of a polycondensate, in particular, a polyamide, by adding, specifically, a pore-forming agent, however, have still not been addressed and resolved by the prior art. Problems still arise in terms of the incorporation of the pore-forming agent in a manner which results in uniform distribution and, hence, uniform expansion of the product. Several tecnhiques can be employed, each of which exhibits marked disadvantages.
One technique involves preparing a composition in a slow mixer and then granulating the resulting mixture. In this case, it is necessary to use a pore-forming or blowing agent which has a decomposition point higher than the temperature required for granulating the polycondensate. The choice of a suitable pore-forming agent, therefore, is very restricted.
It is also possible to prepare a simple mixture of powdered pore-forming agent and polycondensate by various known means. The very small amount of pore-forming agent, and also its structure, inevitably lead to a poor distribution of the pore-forming agent which manifests itself in the non-uniformity of the product's structure. This non-uniformity is evident, whether within a simple product shaped article or between or among the different shaped articles resulting from a mass production operation.